Cerebral Microvascular Hemodynamics and its Regulation Studied by a Laser-Doppler Method

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This research project was aimed to analyze the blood flow dynamics and its regulation of cerebral microcirculation using our developed fiber-optic laser-Doppler anemometer microscope (FLDAM). The FLDAM measures the cross-sectional mean velocity in a single microvessel with high temporal and spatial resolutions. It is suitable for surface microcirculation of solid organs like brain, because it operates under a back scatter mode and the light source is intense.In this study, the FLDAM has been further improved in its temporal resolution up to 1 ms and in the limits of velocity range up to 200 mm/s, so that it can measure pulsatile velocity in the pial arterioles with diameter larger than 100 μm. Actually, they were confirmed by measuring the temporal changes of velocity in the gerbil pial arterioles during a whole brain ischemia-reperfusion by occluding the bilateral common carotid arteries. The velocity first decreased to about 0 during the period of maximal vasoconstriction and then in … More creased to about double the control velocity (a few 10 mm/s) after reperfusion.Effects of nitric oxide (NO)(L-arginine intake) on the cerebral microcirculation in stroke-prone spontaneously hypertensive rats were investigated by the FLDAM.The diameter, mean blood velocity and wall shear rate in the pial arterioles with diameter larger than 20 μm decreased significantly from 4 to 12 weeks of age for the control group, while they decreased less significantly for the L-arginine group. Plasma NO concentration also decreased significantly from 4 to 12 weeks for the control group, while the decrease was less significant for the L-arginine group.Since the optical coherence tomography (OCT) can measure the internal structure of highly scattering medium to 2-3 millimeters in depth with a spatial resolution about 10 μm, OCT microscope system was developed for the purpose of in vivo 3-dimensional imaging of microvascular as well as neural networks in the cerebral cortex. The in vitro observation of microvessels in the rat mesentery preparation demonstrated its imaging capability. The spatial resolution was found to be 14 μm (lateral) by 16 μm (longitudinal) and the imaging depth was larger than 600 μm. Less